Muffler for impeller with rearwardly curved blades

ABSTRACT

A high speed centrifugal air impeller assembly with rearwardly curved blades has it impeller backplate directly cooperating with an adjacent housing wall portion to provide a narrow annular sound attenuating passageway from an impeller chamber to a motor and discharge chamber.

RELATED APPLICATIONS

Provisional Application No. 60/508,325, titled “Internal Muffler forBackward Inclined Blower” filed Oct. 2, 2003, inventor David A. Curtis,incorporated herein by reference.

BACKGROUND OF INVENTION

This invention relates to a high speed centrifugal air impeller withrearwardly curved blade and more particularly to sound attenuation meanstherefore. Impellers of the type under consideration are relatively lowflow high speed devices, which operate in the neighborhood of a bladetip speed up to approximately 550 feet per second.

Air flow is three dimensional. Air enters the impeller axially throughinlet openings in the housing and impeller. In the plane of rotationthere is a circulation that flows outwardly and is collected by thehousing for approximately 300 degrees of rotation. Typically an outletsection makes up the remaining flow, usually a cylindrical section whoseaxis is substantially tangent to the impeller outer diameter.

As will be apparent, the high speed operation of these devices resultsin substantial noise generation. One method of noise reduction usedinvolved the provision of an impeller housing having two discretechambers, one containing the impeller and the other the air outlet ordischarge section. Thus, a muffler effect can be provided for by meansof a rapidly changing cross-sectional opening. In the prior art adivider piece is provide in one design and cooperates with the impellerbackplate to define a narrow annular opening spaced radially inwardlyfrom the housing wall but interconnecting the impeller and dischargechambers. Sound waves passing through the opening along with the air aresubstantially attenuated. The additional part, however, addssignificantly to manufacturing cost and assembly complexity and theoverall cost of the impeller assembly is adversely affected.

It is the general object of the present invention to provide a highspeed centrifugal air impeller assembly having rearwardly curved bladeswith improved sound attenuation means which can be manufactured ateconomic advantage and which also enhances impeller performance.

In fulfillment of the foregoing object and in accordance with thepresent invention, an impeller housing is provided with air inlet anddischarge openings. An air impeller with an annular backplate isdisposed in the housing with a circumaxially spaced series of longnarrow rearwardly inclined air moving blades on its backplate and withits inlet opening in communication with the housing inlet opening. Theannular backplate of the impeller cooperates with an annular potion ofthe housing inner surface to define a narrow annular passageway anddiscrete chambers on opposite sides thereof. Although the impeller maybe otherwise driven, it preferably has its backplate connected with anddriven by an electric motor mounted in the chamber on the side oppositethe blades. With this arrangement, the air flow created by the impellerblades is constrained to flow through the narrow annular passagewayconnecting the impeller and motor chambers and the sound wavesaccompanying the flow are substantially attenuated in flow through thepassageway. It should also be noted that the air flow is not required toreverse direction on reaching the housing wall in order to flow radiallyinwardly and then through the annular passageway as the prior artdesign. Confinement of the motor in its chamber within the housing alsocontributes significantly to overall sound reduction.

DESCRIPTION OF DRAWINGS

FIG. 1 of the drawings shows a prior art design in sectional schematicform,

FIG. 2 illustrates the improved design of the present invention also insectional schematic form.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring initially to FIG. 1, it will be observed that an impellerhousing is indicated generally at 10. Mating upper and lower cup-shapedmembers form a generally cylindrical housing with an annular thirdhousing member 15 clamped therebetween. The member 15 has a radiallyinwardly projecting annular extension 16 which cooperates with animpeller backplate 18 to define an annular passageway 20 spaced radiallyinwardly from the inner wall of the housing 10. The extension 16 and thebackplate 18 cooperatively define upper and lower chambers 22 and 24 inthe housing and the latter carries a circumaxially spaced series of longnarrow rearwardly curved air moving blades 26,26. A housing inletopening 28 receives an inlet member 30 of the impeller and the air isconducted generally radially outwardly where it is forced to reversedirection at the housing wall and travels radially inwardly beforepassing through the passageway 20 to the upper chamber 22. The chamber22 contains electric motor 32 driving the impeller through connectionwith backplate 18 and a discharge opening 34, which extends in adirection generally tangent to the housing wall.

As will be apparent, a degree of sound attenuation will be realized withthe design of FIG. 1. As mentioned above, however, it will also beapparent that the third housing part 15 will add substantial cost inmanufacturing and assembly time. Further, the inefficient reversing flowpattern is obviously detrimental to impeller performance.

Referring now to FIG. 2, the improved impeller assembly of the presentinvention has a housing indicated generally at 40 which may vary widelyin form but which preferably comprises a pair of mating cup-shapedmembers 42,44 as in FIG. 1. The members 42,44 are attached directly toeach other at their open ends to provide a desirably simple two partconstruction. At the junction between the members on the interiorsurface of the housing a narrow annular portion 46 thereof is providedirrespective of the remaining configuration of the housing. This portionof the housing cooperates with an enlarged backplate 48 to define anarrow annular air passageway 50 for the passage of air and theattenuation of accompanying noise. The backplate also serves to define alower chamber 52 which houses an impeller 54 and from which air flowsthrough the passageway 50 to an upper chamber. The lower surface of thebackplate 48 also carries a circumaxial series of long narrow rearwardlyinclined air moving blades 56,56 and an inlet tube 58 which is receivedin inlet opening 60 in the lower wall of the housing member 44. As willbe apparent, air drawn inwardly through the inlet tube 58 will bedischarged radially outward from the impeller blades and will then makea direct right angle turn through the passageway 50 without any reversalin flow and resulting turbulence.

As mentioned above, various configurations may be employed for thechambers 52, 54. In this regard it should be observed that the diameterof the narrow annular portion which defines the opening 50 incooperation with the backplate 48 should in all cases be at least aslarge as that of the inlet chamber 52.

The upper chamber 54 preferably houses an electric motor 62 for rotatingthe backplate of the impeller and thus driving the impeller. Alsolocated in the chamber 54 is a discharge tube which has its axissubstantially tangent to the wall of the housing. As mentioned confiningthe electric motor in the housing also serves to reduce noise generatedby the assembly.

1. A high speed centrifugal air impeller assembly with rearwardly curvedblades and with sound attenuation means; said impeller comprising ahousing defining air inlet and air discharge openings, an air impellerwith an annular backplate carrying a circumaxially spaced series of longnarrow rearwardly inclined air moving blades on one side disposed in thehousing with it inlet opening in communication with the housing inletopening, said backplate also defining discrete impeller and motorchambers in the housing, an electric motor mounted in the motor chamberon an opposite and discharge side of the backplate in drivingrelationship therewith, said housing having an annular portion of itsinner surface adjacent said backplate and said backplate having an outerdiameter slightly less than the inner diameter of said housing annularportion to define therewith a narrow annular air passageway immediatelyadjacent the housing inner surface and which interconnects the impellerand motor chambers and provides sound attenuation during the passage ofimpeller discharge air therethrough.
 2. A high speed centrifugal airimpeller as set forth in claim 1 wherein the ratio of the annular areabetween the backplate and housing to that of the annular area betweenthe blade tips and housing falls in the range 0.10 to 0.50.
 3. A highspeed centrifugal air impeller as set forth in claim 1 wherein theimpeller is operated at a tip speed up to approximately 550 feet persecond.
 4. A high speed centrifugal air impeller as set forth in claim 1wherein the backplate extends substantially beyond the outer diameter ofthe blades.
 5. A high speed centrifugal air impeller as set forth inclaim 1 wherein the housing is formed of a pair of mating cup shapedparts, and wherein said annular portion of the inner surface of thehousing resides at the junction of the two parts.
 6. A high speedcentrifugal air impeller assembly with rearwardly curved blades and withsound attenuation means; said impeller comprising a housing defining airinlet and air discharge chambers respectively having inlet and dischargeopenings, an air impeller with an annular backplate carrying acircumaxially spaced series of long narrow rearwardly inclined airmoving blades on one side disposed in the housing with its inlet openingin communication with the housing inlet opening, said housing alsohaving an annular portion at its inner surface adjacent said backplatewith a diameter slightly greater than that of the backplate and at leastas large as that of the inlet chamber to define a narrow annular airpassageway adjacent the housing inner surface interconnecting the inletand discharge chambers and providing sound attenuation during thepassage of impeller discharge air therethrough
 7. A high speedcentrifugal air impeller as set forth in claim 6 wherein the ratio ofthe annular area between the backplate and housing to that of theannular area between the blade tips and housing falls in the range 0.10to 0.50.
 8. A high speed centrifugal air impeller as set forth in claim6 wherein the impeller is operated at a tip speed up to approximately550 feet per second.
 9. A high speed centrifugal air impeller as setforth in claim 6 wherein the backplate extends substantially beyond theouter diameter of the blades.
 10. A high speed centrifugal air impelleras set forth in claim 6 wherein the housing is formed of a pair ofmating cup shaped parts, and wherein said annular portion of the innersurface of the housing resides at the junction of the two parts.